Solvent extraction of lubricating oils with phenol



United States Patent @hfice 2,857,326 Patented Oct. 21, 1958 SOLVENT EXTRACTION F LUBRICATING OHS WITH'PHENOL Bruce C. Benedict, Bartlesville, Okla., assignor to Phiilips Petroleum Company, a corporation of Delaware No Drawing. Application December 9, 1954 Serial No. 474,270

4 Claims. (Cl. 20 832 3) This invention relates to solvent extraction. In one aspect it relates to an improved process of solvent extraction wherein contacting and phase separation are carried out in a centrifugal treating zone. In another aspect it relates to a solvent extraction process carried out in a centrifugal treating zone wherein oils of improved properties and in increased yields are produced.

One of the distinctive characteristics of a lubricating oil is its viscosity. Its usefulness as a lubricant depends at least in part upon its viscosity. Its usefulness as an automotive lubricant depends further upon viscosity change with temperature. An oil which decreases in viscosity to a greater extent than another oil is less desirable as an automotive lubricant. Conversely an oil which thickens more with decrease in temperature than another oil is also a less desirable automotive lubricant. A measure of the ability of a lubricating oil to thin out upon increase in temperature and to thicken upon decrease in temperature is termed the viscosity index of the oil. On oil having a high viscosity index, that is, a large number, for example 100, is one which thins out less with increase in temperature and thickens less with a decrease in temperature than an oil having a lower viscosity index, for example 80. The term viscosity index is well understood in the lubricant art and further explanation of this term is deemed unnecessary.

One of the chief sources of concern to the lubricating ,oil refiner is the preparation of lubricating oils having high viscosity indices-and at the same time obtaining satisfactory yields of the oils by solvent extraction. In order to produce a superior automotive lubricating oil from petroleum fractions those components present which are undesirable, that is, unsaturated, aromatic and/or naphthenic in structure are separated from the constituents which are desirable, i. e., paraflinic in structure. Solvent extraction is one of the methods employed to separate the above mentioned undesirable constituents from desirable paraflinic constituents. Various systems have been suggested for improving the efliciency of treating the oil with selective solvents, as regards viscosity index and. oil yield. For liquid-liquid extraction of lubricating oils and other hydrocarbon mixtures, various types of contactors have been used, such as liquid-liquid extraction columns. operated either batchwise or countercurrently, mixers and liquid-liquid contactors of various types. One type of liquid-liquid contacting apparatus employed is a centrifugal contactor.

An object of my invention is to provide an improved process for solvent extracting hydrocarbon mixtures containing paratfinic and non-paraffinic hydrocarbons for separation of one of these types of hydrocarbons from the other.

Another object of my invention is to provide a solvent extraction process for separating non-parafiinic hydrocarbons from mixtures of these with paraflinic hydrocarbons.

Still another object of my invention is to provide such a process which is economical to operate and which requires small contacting equipment.

Yet another object of my invention is to provide an improved process involving use of a centrifugal contacting and separating apparatus for solvent extracting hydrocarbon oils.

Still another object of my invention is to provide such a process for the production of a highly paraffinic lubricating oil of improved properties and in increased yield compared to known processes.

These and other objects will be realized upon reading the following full and complete description of my process.

I accomplish these andother objects and advantages by providing a countercurrent liquid-liquid solvent extraction process in which a hydrocarbon mixture containing at least one paraffinic hydrocarbon and at least one non-paraifinic hydrocarbon is treated for the separation of said hydrocarbons, comprising, adding Water to the hydrocarbon mixture, introducing the hydrocarbon mixture and added water into a centrifugal liquidliquid treating zone, introducing an extraction solvent in which water is at "least partially miscible into said zone, and Withdrawing a raflinate phase and an extract phase separately from said zone.

It is known that water can be injected into the extract phase near the bottom or extract outlet end of a countercurrent solvent extraction column, in which a mixture near the extractoutlet end of a phenol extraction column, the solubility of the oily contents in the solvent is modified and the more parafiinic constituents in solution in the solvent are precipitated as a finely divided oily phase. Since most solvents are specifically heavier than hydrocarbon oils undergoing extraction the precipitated more parafiinic constituents rise in the column.

This precipitated more parafiinic oily phase on rising upward through the column serves as reflux. The use of such internal reflux results in an increased yield of rafiinate oil having improved properties. 'In some centrifugal contactor apparatus for contacting a pair of at least partially immiscible liquids there are usually only two inlet and two outletv ports. One inlet port is for inlet of materials to be extracted, .the other inlet port is for inlet ofextraction solvent, one outlet port is for outlet of nndissolved constituents while the second outlet port is for the :solution. of solvent and dissolved constituents. In order to obtain the benefits of operating with reflux, for. example, specifically with water, several methods have been proposed or employed. One method proposed involves the use of two centrifugal contactors in series, with water .being injected into the extract phase removed .from the first centrifugal contactor and the mixture of water and extract being charged into the second contactor. "The oil precipitated in the second contactorflis separated from the extract phase and is returned to the oil feed line to the first contactor. A second method proposedinvolvesnthe use of an outside mixing and settling vessel wherein the extract from the contactor is-mixed, the Water and the precipitated oil separated, and the rejected oil .is charged with the oil feedto the contactor. A third proposal involves providing a third inlet port and a liquid introduction tube into a centrifugal contactor for the inlet of water. All of these methods involved considerable additional equipment and therefore increase the expense of operation.

In accordance with the invention, 1 have found that I can increase the yield of high viscosity index lubricating oil raffinates in the phenol extraction of lubricating oil stocks with a centrifugal contactor by the addition of water to the charge oil. In carrying out the process I merely add water to the oil feed stock continuously as the oil feed stock is being introduced into the contactor.

Such a contactor, suitable for practicing the process of my invention, is fully described in U. S. Patent 2,670,132. With highly aromatic oils, 1 add as much as 15-20 percent Water by volume based on the volume of the solvent phenol used. With more parafiinic lubricating oils the proportion of water required is considerably less than the amounts just mentioned. As little as 2 percent by volume of water or even less, for example, as little as /2 to 1 percent water by volume based on the volume of the solvent is sufficient for producing improved highly paraifinic lubricants by phenol extraction. The ratio of water employed is also dependent upon the degree of refinement desired.

When phenol is used in the extraction of the herein described lubricating oil stock the phenol-to-oil ratio employed is varied from 0.5:1 to 5:1 and preferably a ratio of about 1:1 to 3:1 is employed. The temperature employed in this extraction generally ranges from about 100 F. to about 250 F., preferably from about 125 F. to about 225 F. Sufiicient pressure is maintained on the centrifugal contactor to insure liquid phase contacting.

The centrifugal contactor, mentioned above as being fully described in said Patent 2,670,132 will be herein described only briefly. In this contactor a cylindrical rotor is mounted on a horizontal shaft. This rotor is designed to rotate at a constant speed on any setting between 2500 R. P. M. and 5000 R. P. M. The heavy liquid stream, for example, phenol, is introduced into the extractor at the hub of the rotor through the center of the horizontal shaft from one side of the rotor. The specifically light liquid, which in this case is the lubricating oil charge stock and water, is introduced through the shaft on the other side of the rotor and through a machined channel from which it enters the extraction zone. The heavy liquid is forced outward and toward the periphery of the rotor by centrifugal force while the specifically light liquid works its way from the periphery toward the shaft thereby contacting very intimately the light liquid with the heavy liquid. The contacting zone is provided with a plurality of bafiles or concentric ringlike trays which contain numerous small slots through which both liquids must flow. These slots are staggered from baffle to battle so that the path followed by the liquids will be a tortuous one. There is also provided a settling space adjacent the hub and one adjacent the periphery of the rotor. In the operation of this contactor there is a liquid-liquid interface on each of the ring trays and the respective liquids after being separated from one another in a space between two adjacent ring trays flow through the respective slots in said trays to spaces intermediate these trays and the next trays in the direction of the flow of the liquids. When the extraction solvent is for example, phenol, which is specifically heavier than the liquid being extracted, the raffinate is withdrawn from the settling space adjacent the hub of the rotor through a back pressure regulator which regulates the relative quantity of heavy and light liquids in the contacting Zone. The extract, which is the specifically heavy phase, is withdrawn from the settling space near the periphery of the rotor through a machined channel more or less similar to the above mentioned channel through which the feed oil is introduced. A regulator is not ordinarily needed for controlling the withdrawal of the extract phase.

While my invention is described in connection with the phenol extraction of a lubricating oil stock employing a centrifugal contactor, it is contemplated that the invention is applicable to the extraction of other hydrocarbon mixtures such as petroleum naphthas, higher boiling portions of cracked and reformed gasolines, kerosene and the like.

While I have described my invention relative to the use of phenol as the extraction solvent, other suitable extraction solvents in which water is at least partially miscible are also used. Other suitable solvents are, for example, methyl cellosolve, and diethylene glycol provided the conditions laid down herein are fully met.

EXAMPLE A centrifugal contactor, as described in the above mentioned patent, was used for the phenol extraction of a midcontinent raw lubricating oil stock using both aqueous and anhydrous phenol as solvents, and water added to oil feed. The crude oil stock from which the lubricating oil fraction was prepared was a mixture of 60 percent Ellenberger (Texas), 20 percent Burbank (Oklahoma) and 20 percent West Edmond (Oklahoma). The bottoms from this crude oil mixture was treated for recovery of the above mentioned lubricating oil stock. The raw lubricating oil stock had the following properties, before and after dewaxing.

In extracting this raw oil stock according to my process and in the runs made for comparative purposes a USP grade phenol was used. Extraction temperatures ranged from about F. to about F. The extraction runs, the data of which are given in Table II. were made on a laboratory size centrifugal extractor, such as that described in the above mentioned patent. Suitable oil heaters were provided to heat the oil feed and the solvent streams of the contactor. The rotor of the contactor was 18 inches in diameter and 1.75 inches wide and contained 22 settling zones and 21 mixing zones. All of the runs herein reported were made at 80 percent of the flooding rate of the contactor, which rate was the value recommended by the manufacturer as the most efficient.

Run No. 1 had water added to the feed oil stock in an amount equal to 8 percent of the solvent phenol. When the results of run No. 1 are compared to the results of run No. 4 in which run the solvent phenol contained 8 percent water in solution, it will be noted that the yield of rafiinate was'0.6 percent higher and the viscosity index was 1.1 units greater. Thus, it is seen that when water is added to the oil charge stock and this mixture then centrifugally treated with extraction solvent and the mixture centrifugally separated into extract phase and raffinate phase, the rafiinate oil recovered from the railinate phase is of improved viscosity index and in higher yield than when the water was previously dissolved in the solvent (run No. 4). When a lubricating oil refiner is producing a lubricant meeting viscosity index specification an oil having a viscosity index of 1.1 units higher than another oil obviously requires less viscosity index improver. Likewise, an increase in yield of rafllnate oil of 0.6 volume percent at first appears to be a very small increase in yield but when considered from point of view of an extraction plant producing, for example, from 2000 to 5000 barrels per day a small increase in yield amounts to many dollars per day. Extraction conditions which cause an increase in viscosity index of the rafiinate oil commonly decrease the raflinate oil yield, and vice versa. In my invention, however, I obtain an increase in rafiinate oil viscosity index and a simultaneous increase in yield. Thus the improvements indicated by the raffinate oil of run No. 1 are real and tangible. Run No. 4 is shown herein for comparative purposes and it is to the rafiinate oil of this run that applicants run No. 1 was compared. Run No. 2 shows that when anhydrous phenol was used as the extraction solvent without the addition of water in any form whatever the viscosity index of the rafl'inate oil was quite high, but the yield of oil recovered was uneconomically low. Run No. 3 was shown to illustrate the value of the use of an intermediate quantity of water with the phenol. Thus, when 2.5 percent water was used with the phenol the viscosity index was intermediate runs 1 and 2 and likewise a yield of raflinate oil was also intermediate the yield of oil from runs 1 and 2.

It will be obvious that many operating conditions can be varied without materially departing from the spirit and scope of my invention as, for example, the speed of the rotor of the centrifugal contactor can be changed between wide limits as a function of, for example, the viscosity of the oil feed stock being extracted. Because a lubricating oil stock is of relatively high viscosity and is more difficult to mix with an extraction solvent when treating such an oil, the rotor should be operated at a higher number of revolutions per minute than when a low viscosity gasoline or naphtha is being treated.

While certain embodiments of this invention have been described for illustrative purpose the invention obviously is not limited thereto.

I claim:

1. In a countercurrent liquid-liquid solvent extraction of a lubricating oil stock containing at least one paraflinic hydrocarbon and at least one nonparaflinic hydrocarbon for the production of a paraflinic lubricating oil, the improvement comprising adding water to said oil stock, introducing this oil stock and water mixture into a centrifugal liquid-liquid treating zone, introducing solvent phenol into said zone and therein centrifugally contacting said mixture with said phenol, and withdrawing a raffinate phase and an extract phase separately from said zone, the phenol-to-oil stock ratio being from about 0.5:1 to 5:1, and the water added to said oil stock being from about 0.5% to about 20% by volume based on the volume of the phenol.

2. In a countercurrent liquid-liquid solvent extraction of a lubricating oil stock containing at least one paraflinic hydrocarbon and at least one nonparaffinic hydrocarbon for the production of a parafiinic lubricating oil, the improvement comprising adding Water to said oil stock, introducing this oil stock and water mixture into a centrifugal liquid-liquid treating zone, introducing solvent phenol into said zone and therein centrifugally contacting said mixture with said phenol, and withdrawing a raffinate phase and an extract phase separately from said zone, the phenol-to-oil stock ratio being from about 0.5 :1 to 5:1, and the water added to said oil stock being from about 2% to about 20% by volume based on the volume of the phenol.

3. In a countercurrent liquid-liquid solvent extraction of a lubricating oil stock containing at least one parafiinic hydrocarbon and at least one nonparaffinic hydrocarbon for the production of a paraflinic lubricating oil, the improvement comprising adding water to said oil stock, introducing the oil stock and water mixture into the outlet end of a centrifugal liquid-liquid contacting zone having an inlet end and an outlet end as regards the flow of solvent, introducing solvent phenol into said inlet end of said zone and therein contacting said oil stock and water mixture with said phenol, removing ratfinate phase from said inlet end and removing extract phase from the outlet end of said zone, the phenol-to-oil stock ratio being from about 0.5:1 to 5:1, and the water added to said oil stock being from about 0.5% to about 20% by volume based on the volume of the phenol.

4. In a countercurrent liquid-liquid solvent extraction of a lubricating oil stock containing at least one parafiinic hydrocarbon and at least one nonparaffinic hydrocarbon for the production of a parafiinic lubricating oil, the improvement comprising adding water to said oil stock, introducing the oil stock and water mixture into the outlet end of a centrifugal liquid-liquid contacting zone having an inlet end and an outlet end as regards the flow of solvent, introducing solvent phenol into said inlet end of said zone and therein contacting said oil stock and water mixture with said phenol, removing rafiinate phase from said inlet end and removing extract phase from the outlet end of said zone, the phenol-to-oil stock ratio being from about 0.5:1 to 5:1, and the water added to said oil stock being from about 2% to about 20% by volume based on the volume of the phenol.

References Cited in the file of this patent UNITED STATES PATENTS 1,908,018 Henderson May 9, 1933 2,176,983 Thayer Oct. 24, 1939 2,246,297 Duncan et al. June 17, 1941 2,302,383 Stratford et al. Nov. 17, 1942 2,324,952 Read July 20, 1943 2,444,582 Smith July 6, 1948 2,645,596 Axe July 14, 1953 

1. IN A COUNTERCURRENT LIQUID-LIQUID SOLVENT EXTRACTION OF A LUBRICATING OIL STOCK CONTAINING AT LEAST ONE PARAFFINIC HYDROCARBON AND AT LEAST ONE NONPARAFFINIC HYDROCARBON FOR THE PRODUCTION OF A PARAFFINIC LUBRICATING OIL, THE IMPROVEMENT COMPRISING ADDING WATER TO SAID OIL STOCK, INTRODUCING THIS OIL STOCK AND WATER MIXTURE INTO A CENTRIFUGAL LIQUID-LIQUID TREATING ZONE, INTRODUCING SOLVENT PHENOL INTO SAID ZONE AND THEREIN CENTRIFUGALLY CONTACTING SAID MIXTURE WITH SAID PHENOL, AND WITHDRAWING A RAFFINATE PHASE AND AN EXTRACT PHASE SEPARATELY FROM SAID ZONE, THE PHENOL-TO-OIL STOCK RATIO BEING FROM ABOUT 0.5:1 TO 5:1, AND THE WATER ADDED TO SAID OIL STOCK BEING FROM ABOUT 0.5% TO ABOUT 20% BY VOLUME BASED ON THE VOLUME OF THE PHENOL. 